Grilles which are installed at a door or a window opening to bar unauthorized entry into a room can present problems when it is necessary to use the barred area as an emergency exit, as might occur, for example, in the case of a fire within the building. In order to leave a building through an opening provided with a protective grille, it is necessary to have either means for completely removing the grille or means to swing one end of the grille away from the opening as by hinging the other end. In order to prevent someone from moving the grille or swinging it open from a position outside of the building, some devices have required the use of key-actuated locking means. It is highly desirable to avoid the use of keys because of the possibility that the key might not be available when it is necessary to exit through the window. A need exists for a security system for a window which includes a grille wherein the grille is readily and quickly openable only by a person on the inside and which may be opened without any special tools or keys.